In recent years, an over-the-top video (OTT-V) is dominant as a streaming service on the Internet. As a fundamental technology for the OTT-V, the moving picture experts group phase-dynamic adaptive streaming over HTTP (MPEG-DASH) is recently widespread (for example, see Non-patent Document 1).
In the MPEG-DASH, a distribution server prepares video data groups having different screen sizes and encoding rates for one piece of video content, and a reproduction terminal requests a video data group having an optimum screen size and encoding rate according to circumstances of a transmission path. Thus, adaptive streaming distribution is achieved.
Incidentally, it is desired that forensic information be embedded into the data of video content as countermeasures against the illegal distribution of video content. An example of forensic information is a plurality of variations (patterns) prepared regarding at least part of the data of video content each being encrypted with a unique key.
When forensic information is embedded in video content, and only one key is provided to a reproduction apparatus, a reproduction apparatus from which an illegal copy has been distributed can be identified by finding a key corresponding to a pattern contained in the illegal copy when an output reproduced by a specific reproduction apparatus has been illegally copied.